| Author |
Message |
    
Wolverine
Intermediate Member
Username: Wolverine
Post Number: 325
Registered: 2-2003
| | Posted on Friday, February 25, 2005 - 8:22 am: | 
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How small can a groundplane actually be? And for that matter how large can a groundplane be?. I have 40 channel walkie talkies that I use sometimes, where is the groundplane in a walkie talkie, that makes it talk ( is it he chassis itself)?. Would a sheet of aluminum or steel, say 2 feet square be considered a ground plane?. I understand why car vehicles are groundplanes, and even outdoor antennas, but Firestick has an indoor antenna on it's website that is supposed to work better than a dipole. It's a 5' whip sitting on 3 or 4 rods (Radials). Where is the groundplane to make this antenna work? Is it the rods that the whip is sitting on? Somebody has got to explain this to me. Thanks in advance.
Wolverine. |
1861
Member
Username: 1861
Post Number: 91
Registered: 2-2004
| | Posted on Friday, February 25, 2005 - 2:14 pm: |
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I DON,T KNOW , BUT HAVE BEEN TOLD THAT YOUR BODY IS THE GROUND PLANE FOR WALKIE TALKIE . |
Racer_x
Junior Member
Username: Racer_x
Post Number: 40
Registered: 2-2005
| | Posted on Friday, February 25, 2005 - 8:15 pm: |
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That's true, your body does act as the ground plane for a handheld. I've also used a 1/4 wavelength pigtail of wire wrapped around the BNC jack to act as a counterpoise and it works pretty well.
You only need a ground plane or counterpoise for a 1/4 wavelenth whip. The 1/4 wavelength counterpoise makes the 1/4 wavelength antenna resonant. 1/2 wave and 5/8 wave antennas are already resonant and don't need a counterpoise, although they do change the pattern somewhat and act to decouple RF from the feedline.
A counterpoise should be 1/4 wavelength or longer. I've used sheets of aluminum foil with a magnet mount mobile as a counterpoise and it's worked well.
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Kj7gs
Junior Member
Username: Kj7gs
Post Number: 19
Registered: 12-2004
| | Posted on Friday, February 25, 2005 - 9:36 pm: |
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Wolverine, I read an article a couple of years ago that stated that a vertical quarter-wave antenna can have as little as 2 radials, as short as 1/8 of a wavelength each (shorter than that significantly reduces bandwidth), as long as they're brought back into resonance with a coil.
The article says that soil conductivity and dielectric constant affects the radiation pattern out to tens of wavelengths in each direction, which is why the ideal location for a vertical antenna is over saltwater. Obviously you can't do much about the ground that you're placing your vertical on, but it's also pointless to stretch out miles and miles of copper when the solution in the above paragraph will work just fine!
As to your third question, I've never taken an antenna analyzer to a walkie-talkie antenna, but I really don't know that a 50-ohm load is even a requirement. Since the antenna is directly connected to the radio, there is no SWR to worry about. The walkie-talkie antenna isn't a very efficient radiator, but I've never seen a walkie-talkie with a 9' whip attached anyway (or double that, for an end-fed design).
I don't know what dipole characteristics Firestik's vertical is being compared to, but they both have very different radiation patterns anyway. The rods on the tripod make up the counterpoise for the vertical. But I don't know how long they are or if they are helically wound to provide what the vertical wants to "see". If those radials are at least 4-1/2 feet each, then that would seem to fit with what I said in the first paragraph. |
Pig040
Advanced Member
Username: Pig040
Post Number: 712
Registered: 7-2003
| | Posted on Saturday, February 26, 2005 - 10:39 am: |
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Hey wolverine,
When I first got my 2meter radio, I didnt have an antenna for it except a mobile, so I put a cakepan on top of a fencepost, and put the magnet mount on it, worked fine for 2m!
Rich |
Wolverine
Intermediate Member
Username: Wolverine
Post Number: 326
Registered: 2-2003
| | Posted on Tuesday, March 01, 2005 - 4:46 am: |
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Thanks all. I'm going to purchase a flat sheet of steel or aluminum (Not foil). It's going to be about 2 to 3 ft square, then I'm going to put a mag-mount in the middle. I'm thinking about trying to mount a big coil antenna, instead of a whip. This will be an indoor apartment antenna set-up. I just hope that the sheetmetal 2 to 3ft sq, will be enough.
Wolverine. |
Racer_x
Member
Username: Racer_x
Post Number: 66
Registered: 2-2005
| | Posted on Tuesday, March 01, 2005 - 7:10 pm: |
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Wolverine - It won't give you a good match for transmitting. You need a full 1/4 wave for an effective counterpoise - even if it's just a couple of wires.
I realize it isn't pretty, but the foil works fine. I've used it to make an antenna. |
Kj7gs
Junior Member
Username: Kj7gs
Post Number: 20
Registered: 12-2004
| | Posted on Tuesday, March 01, 2005 - 8:49 pm: |
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I agree with Racer X, I doubt if you'll get a very good match from that configuration. I may not have stressed the importance of a coil for a counterpoise 1/8 to 1/12 of a wavelength, but 3-4 feet in all directions will definitely require one! |
Road_warrior
Intermediate Member
Username: Road_warrior
Post Number: 320
Registered: 7-2004
| | Posted on Tuesday, March 01, 2005 - 8:25 pm: |
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The radials on the Firestik indoor
antenna is its groundplane.
Jim/CEF 375/PA |
Road_warrior
Intermediate Member
Username: Road_warrior
Post Number: 324
Registered: 7-2004
| | Posted on Wednesday, March 02, 2005 - 12:42 am: |
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Do you have to run a indoor antenna?
Man, theres nothing like having one outside./
Years ago i lived in an apartment, i took a
car tire rim & mounted a 102" steel whip
to it, had a groundwire coming off it & just
sat it on my porch roof./ worked good for what
it was./ But, nothing beats those outside
base antennas.
JIM/PA/CEF375 |
Wolverine
Intermediate Member
Username: Wolverine
Post Number: 330
Registered: 2-2003
| | Posted on Wednesday, March 02, 2005 - 2:14 am: |
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Okay Road warrior, and Racer X, if I used a Big Coil antenna on a mag-mount sitting on top of the radials of the firestick indoor antenna, would that work, and would it match well??.
Wolverine. |
Road_warrior
Intermediate Member
Username: Road_warrior
Post Number: 325
Registered: 7-2004
| | Posted on Wednesday, March 02, 2005 - 1:01 pm: |
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Sitting a mag mount on radials will probably
not work. Where are you putting this antenna?
Attic, upstairs, downstairs ect.???
My uncle has 2 cophased K-40's in his attic
with runs of foil for his groundplane. It took
him lots of experimenting with it./ But,
hes going to be mounting an outside antenna
soon as hes just not happy with performance.
If your needs are simple & all you want is
an inside antenna or it has to be that way.
You will have to experiment to find what
works best for you./ Since everybodies
situation is quite different, i can't
tell you want antenna or how much metal
groundplane you will need to achieve best
performance inside your home./
JIM/PA/CEF 375
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Racer_x
Member
Username: Racer_x
Post Number: 75
Registered: 2-2005
| | Posted on Wednesday, March 02, 2005 - 3:09 pm: |
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Probably not - there needs to be a good connection between the radials and the coax shield. How you would manage that with the mag mount and the radials I don't know.
If you're going to buy the indoor antenna then just use it. The big coil antenna isn't going to have any better bandwidth, and if you're planning on running power inside you can forget about that. The interference will be considerable and for health concerns I'd really advise against it. |
Road_warrior
Intermediate Member
Username: Road_warrior
Post Number: 328
Registered: 7-2004
| | Posted on Wednesday, March 02, 2005 - 9:16 pm: |
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I agree with Racer X on his thoughts.
The indoor antenna will probably be just as
good as a mobile antenna./
Having any inside antenna puts limits on what
you can do./ Just get the antenna as high as
possible in your home./ Good Luck!
JIM/PA/CEF 375 |
Wolverine
Intermediate Member
Username: Wolverine
Post Number: 331
Registered: 2-2003
| | Posted on Thursday, March 03, 2005 - 2:56 am: |
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Yeah, you're both right Roadwarrior and Racer X, concerning health concerns and neighbor interference problems if I run an amp. I forgot to mention that I live in a huge 1 bedroom apt, 3 stories up on the third and final floor. So there is no one above me, or buildings in front of me (Looking from my living room window. Maybe I'll just purchase that indoor firestick to see how it does. I'm not really into dipoles, so I'll keep tinkering until I stumble on to something. Thanks.
Wolverine. |
Road_warrior
Intermediate Member
Username: Road_warrior
Post Number: 331
Registered: 7-2004
| | Posted on Thursday, March 03, 2005 - 3:22 pm: |
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Well, your as high as it gets..LOL...
Now, i understand the position your in
living in a apartment. Landlords don't
care for antennas on there roofs...lol
If possible try your antenna near a window.
That helps sometimes./Or mount in on a balcony
if you have one.Good Luck!/ Let us know how
you make out & what worked best for you.
JIM/PA/CEF 375 |
